gprs: Update gprs-sgsn branch to use new msgb->cb layout

The explicit 'tlli, gmmh' members of struct msgb are gone from
current libosmocore and have been replaced by the more generic
'control buffer' mechanism.
diff --git a/openbsc/src/gprs_llc.c b/openbsc/src/gprs_llc.c
index 2c927c6..91b0239 100644
--- a/openbsc/src/gprs_llc.c
+++ b/openbsc/src/gprs_llc.c
@@ -396,7 +396,7 @@
 int gprs_llc_rcvmsg(struct msgb *msg, struct tlv_parsed *tv)
 {
 	struct bssgp_ud_hdr *udh = (struct bssgp_ud_hdr *) msg->l3h;
-	struct gprs_llc_hdr *lh = msg->llch;
+	struct gprs_llc_hdr *lh = msgb_llch(msg);
 	struct gprs_llc_hdr_parsed llhp;
 	struct gprs_llc_entity *lle;
 	int rc;
@@ -409,7 +409,7 @@
 	rc = gprs_llc_hdr_rx(&llhp, lle);
 
 	if (llhp.data) {
-		msg->gmmh = llhp.data;
+		msgb_gmmh(msg) = llhp.data;
 		switch (llhp.sapi) {
 		case GPRS_SAPI_GMM:
 			rc = gsm0408_gprs_rcvmsg(msg);